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Chemical Bonding And Molecular Structure

Question
CBSEENCH11008417
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Bond dissociation enthalpy of H2, Cl2 and HCl and 434, 242 and 431 kJ mol-1 respectively.  Enthalpy of formation of HCl is 

  • 93 kJ mol-1

  • -245 kJ mol-1

  • -39 kJ mol-1

  • 245  kJ mol-1

Solution

C.

-39 kJ mol-1

increment straight H subscript reaction space equals space begin inline style stack sum space Bond space space energy space of space reactant space with space below and space on top end style begin inline style stack sum Bond space space energy space of space product space with space below and space on top end style Here comma space increment straight H subscript straight H minus straight H end subscript space equals space 434 space kJ space mol to the power of negative 1 end exponent increment straight H subscript Cl minus space Cl end subscript space equals space 242 space kJ space mol to the power of minus increment straight H subscript straight H minus Cl end subscript space equals space 431 space kJ space mol to the power of negative 1 end exponent because space 1 half space straight H subscript 2 space plus 1 half Cl subscript 2 space rightwards arrow HCl increment straight H subscript reaction space end subscript space equals space 1 half increment straight H subscript straight H minus straight H end subscript space plus space 1 half increment straight H subscript Cl space minus Cl end subscript space minus space increment straight H subscript straight H minus Cl end subscript equals space 1 half space straight x space 434 space straight x space 1 half space straight x space 242 minus 431 equals space 217 space plus 121 minus 431 equals negative 93 space kJ space mol to the power of negative 1 end exponent

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